1. Field of the Invention
The present invention relates to a disc device for recording and/or reproducing information with respect to a disc having flexibility.
2. Disclosure of Related Art
In recent years, as digital technology has been developed, increasing the capacity of an optical disc has been demanded. An example of a method for increasing the capacity of an optical disc is minimizing the spot diameter of laser light. The spot diameter minimization is realized by increasing the numerical aperture (NA) of an objective lens, in addition to reducing the wavelength of laser light. As the spot diameter is minimized, it is necessary to reduce the distance between an objective lens and a recording surface of an optical disc.
In the conventional optical disc system, however, if the distance between an objective lens and a recording surface of an optical disc is reduced, the objective lens may be contacted with a surface of the optical disc, resulting from rotational displacement at the time of rotating the optical disc at a high speed, and/or an optical pickup or the optical disc may be damaged. Further, in the case where rotational displacement of an optical disc is large, or in the case where an optical disc is rotated at such a high speed as 10,000 times or more per minute to realize a high transfer rate, the optical disc itself may be damaged.
In view of the above, there has been developed an optical disc (hereinafter, called as a “flexible disc”), wherein a recording surface is formed on a thin film having flexibility. Recording and/or reproducing information with respect to a flexible disc is performed by an optical pickup device, after plane displacement of the flexible disc is eliminated. The flexible disc has a feature that the disc can be rotated at a higher speed because the disc weight is reduced by reducing the thickness of a disc substrate, and as a result, an influence by centrifugal force is suppressed.
However, if power supply to the optical disc device is abruptly cut off due to a power outage, a flexible disc which has been kept in a proper state by rotation may be bent toward the optical pickup device, as the rotational speed (the rotation number per unit time, hereinafter simply called as “the rotation number”) is reduced. In this case, the flexible disc and/or the optical pickup device may be damaged by contact. The drawback may also occur in a case that the rotation number of the flexible disc is reduced due to some reason, other than the case where power supply is cut off.